Chevelle Brakes - Whoa Down

Installing a Hard-Stopping, Hydroboosted Four-Wheel Disc Brake System

When it comes to performance upgrades, we all want to make the number; if we're talking stopping distances, we want that number to be small. But it's too easy to focus on the end product rather than the nature of the improvement. For example, we often evaluate braking prowess in terms of simple stopping distance--how rapidly, measured in feet, does the vehicle decelerate from 60 mph to zero? And of course, we were looking for substantially shorter stopping distances when we called on Performance Online (POL) to outfit a big-block-packing Chevelle with its 13-inch big brake kit up front, accompanied by 12-inch rear discs to replace the factory drums, and the necessary master cylinder/prop valve combo to run it. And while we did cut our stopping distances, the fact that we converted this A-body from manual to power brakes by installing a Hydroboost hydraulic brake assist unit taught us that the effort it takes to stop short can be as important as stopping distance itself.

Our subject for this experiment, Jeremiah Becker's '66 'Velle, was fresh out of the paint booth when it graced the cover of our Mar. '07 issue. Becker's ride is actually well-endowed when it comes to suspension, since it's outfitted with a Hotrods to Hell Centerdrive Truckarm rear system, tubular front control arms, and a tall B-body spindle setup. Becker had also added some pretty good rolling stock to his ride, specifically Nitto NT555 Extremes, 245/45ZR17 up front and 285/40ZR17 out back. The braking setup, however, was not particularly high-zoot. The front package included the big single-piston B-body calipers, but these binders were backed up by the factory rear drum brakes and activated by a manual master cylinder. Even so, we actually got a stopping distance of 158 feet out of the old A-body in baseline form.

But it's not always about the bottom line. While we got the most out of the rear drums and B-body front discs and came up with a decent 60-0 number, it took maximum effort to achieve that figure: back arched against the back of the seat, left leg trying to drive the pedal through the floor, driver limping away afterward. More normal braking efforts--think a guy who's just pushing the pedal hoping to stop in a hurry as opposed to someone concentrating on maximum effort--produced considerably longer distances. The setup also faded when subjected to hard use. This is in no way a slam on the brakes our guinea pig came with; the old-school setup was actually pretty effective. Our results simply illustrate the nature of operating a power brake system as opposed to a manual setup. "You need line pressure to stop," says Performance Online's Jim Chadick. "And with a manual system, all you've got to provide it is your leg."

3/20

For all our talk about braking effort and quality as opposed to bottom-line numbers, it was always a given that we would get out and measure before and after braking numbers. For this experiment, we utilized one of Tesla Electronics' G-Tech Pro SS performance meters. It would almost be easier to tell you what this device doesn't do rather than spell out what it does do. It's powered by a car's cigarette lighter or power port and attaches to the windshield with a suction cup. Brake testing is a snap. When performing a normal acceleration run--which is literally as easy as pressing a button and waiting for the signal to start--the unit flashes a red light when the vehicle hits 60 mph, allowing the driver the option of hitting the brakes or continuing on for a full quarter-mile run. The unit's triaxial accelerometer senses when the vehicle is speeding up or rapidly slowing and measures accordingly; the accelerometer also measure handling g-forces on three axes and can display the figures in real time. With a bit more setup, the G-Tech Pro SS can sense and display engine rpm and measure horsepower and torque, and it even has built-in sequential shift lights. This model goes for about $200; the RR model, which has even more features and can upload its data to a PC, is about $300.

Check out this Buick Grand National that gets an upgrade from a Powermaster braking system to a Hydroboost braking system. Read more only at www.gmhightechperformance.com, the official website for GM High-Tech Performance Magazine! » Read More